Microsoft has acknowledged that the April 2025 security updates are causing authentication challenges for certain Windows Server domain controllers, specifically affecting Windows Server versions 2016, 2019, 2022, and 2025. The issues arise after installing the April Windows monthly security update (KB5055523 or later), leading to complications in processing Kerberos logons or delegations that rely on certificate-based credentials. Affected authentication protocols include Kerberos PKINIT, S4U via RBKCD, and KCD. These issues are linked to security measures addressing the critical vulnerability CVE-2025-26647, which allows authenticated attackers to escalate privileges remotely. A temporary workaround involves modifying a registry value. Microsoft has previously addressed similar authentication issues in Windows 11, Windows Server 2025, and earlier versions.